Tertiary alkyl esters such as t-butyl acetate and t-amyl acetate are known useful compounds.
Generally these materials are prepared by acid catalyzed reaction of the tertiary olefin with acetic acid in order to avoid the formation of water and the corresponding equilibrium problems associated with acid-alcohol reactions. See U.S. Pat. Nos. 3,031,495, 3,053,887, 3,173,943, 3,172,905, 3,082,246 and 2,678,332. However, this technology has the problem of olefin polymerization which results in yield loss and purification difficulties. The formation of t-alkyl esters by reaction of the tertiary alkanol with acetic anhydride has been considered but has not found widespread acceptance because it is a slow reaction even when carried out at reflux conditions. The use of catalysts such as Lewis acids or protic acids to improve reaction rates introduces problems of byproduct formation, e.g. alcohol dehydration. U.S. Pat. No. 6,593,491 discloses the formation of t-butyl acetate by reaction of acetic acid, acetic anhydride and MTBE or ETBE with an acid catalyst.
There is a need for a process for the production of t-alkyl esters which is rapid and selective and which lends itself to the ready recovery of reaction products and the recycle of unreacted materials.
Now it has been found that t-butyl acetate and t-amyl acetate can be readily formed in high selectivity and yield by reaction of the t-alkanol with acetic anhydride provided certain catalysts are used and provided that acetic acid is present.